This invention relates to the processing of thin slices of material and, more particularly, to apparatus for automatically removing such slices from a cassette, simultaneously cleaning both sides thereof, and returning the slices to the cassette.
In the processing of semiconductor materials for the ultimate manufacture of integrated circuits and the like, one of the steps required is the cleaning of single-crystal silicon wafers. In years past, such cleaning was performed manually by an operator. An improvement to this manual process is disclosed in U.S. Pat. No. 3,748,677 which discloses semi-automatic apparatus for simultaneously scrubbing both sides of a wafer. The wafers are manually loaded, one at a time, into a rotating disc having pockets formed in the periphery thereof. The disc conveys the wafers between two opposed counter-rotating brushes within a detergent solution spray. After passing the rotating brushes, the wafers drop from the pockets in the disc and float through the detergent bath to a container positioned below the disc. This apparatus possesses a number of disadvantages. In particular, the wafers must be loaded one at a time into the pockets of the disc while other wafers are being scrubbed. Additionally, the wafers are dropped into a bath of the material utilized to clean the wafers, which bath contains impurities just removed from the wafers.
An alternative design in the prior art provides a supply cassette having a plurality of wafers positioned therein. The wafers are removed one at a time from the supply cassette and brought along a series of belts or similar means to a plurality of brushes which scrub both sides of the wafers. The brushes are placed parallel to the direction of movement necessitating rotation of the wafers to enable the entire surface to be scrubbed. The wafers are then conveyed by a series of driven rollers to an air chamber in which the water is blasted off. The wafers are then placed in a second, initially empty, cassette. This is a continuous process with wafers being in various stages of cleaning at any particular time. Unfortunately, this apparatus requires a large amount of space and is very complex in its design. It also requires two cassettes, one being unloaded and the other being loaded.
An improved apparatus is disclosed in our copending application Ser. No. 685,303, filed May 11, 1976, now U.S. Pat. No. 4,062,463, entitled "Automated Single Cassette Load Mechanism for Scrubber" and assigned to the assignee herein, wherein a single cassette is utilized to supply wafers to be cleaned and to receive the wafers after they are cleaned. The apparatus includes a wafer-supporting arm which is movable between a retracted position within the cassette and a scrubbing station for moving a selected one of the silicon wafers from its position within the cassette to the scrubbing station and for returning the selected wafer from the scrubbing station to the cassette. The cassette is located between the retracted position of the arm and the scrubbing station so that the wafer-supporting arm moves from its retracted position to an extended position through the cassette to transfer the selected wafer therefrom and deposit the wafer on a chuck at the scrubbing station. The wafer-supporting arm is then returned to its retracted position while the selected wafer is spun on the chuck and one side of the wafer is cleaned. Then, the wafer-supporting arm is again moved from its retracted position through the cassette to the scrubbing station to receive the cleaned silicon wafer, and is then retracted through the cassette to deposit the cleaned wafer in the cassette. A selection device then operates to move the cassette so that the next wafer to be cleaned is in position to be picked up by the wafer-supporting arm when it is next moved between its retracted position and the scrubbing station. While this apparatus is an improvement in its simplicity over other prior art apparatus, it has the disadvantage that only a single side of the wafer may be cleaned at one time.
It is therefore an object of this invention to provide improved apparatus for automatically and simultaneously cleaning both sides of a silicon wafer.
It is another object of this invention to provide such apparatus wherein only a single cassette is utilized for loading and unloading the wafers to and from a processing station.